Vacuum-tube design



June 16, 1925. 1,542,386

. R. v. L. HARTLEY VACUUM TUBE DESIGN Filed Dec. 14, 1920 Fi i //7 l/emor: 5440b KL fia/ f/ey.

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mm mg mum piz omen, new mnsnr, sss'renon. 'ro m -'nuc conm,;rnconrpnarnn, onnnw roams. Y., A conroiwrron or m p i e "a citizenof the United'zrstates of America the following. is aam11,:c1ear 'concis'e,;and exact descriptiomj residing. atEast Orange, in-the county o vented certain newEandi :use'lfu Improvements in VTacuum-Tubef-Designs, of. which This inventionrelates, to the "design of :electron dischargedevic'es an'd thcir use for the measurement of alternating current, po-' tentials and" has for: an object to'provide an electron; discharge devicexwherein the curve which. represents the relation between the input volta e .and the output current shall have a desired shape. 5

As disclos'edin the patent to Heising No. 1,232,919, July 10,- 1917, a three-electrode audion may be employed for measuring the voltage between two network without taking power from that network and withoutintroducing frequency errors. As disclosed in that patent, the un known potential is measured vby noting the difference in the value of the negative grid potential required to reduce the space current for the tube to zero-when the unknown source is or is not connected to the input circuit of the tube. -The accuracy of that arrangement depends upon the accuracy with which the zero value of space current in the output circuit of. the tube can be determined. .In increasing the negative potential on the gridof' an ordinary audion the current in the output circuit does not characteristic of. the vacuum tube is modizero space current,

fied so that the space current, whe the grid potential is given increasing negative values, approaches a 'zeroj value more rapidly than heretofore, thereby giving a more accurate determination of the value of thenegative grid potentiallrequired to produce This resultis'secured by so spacing'and shaping the grid as to. provide a" greater impedance to the flow of electrons fromthe negative end of thefilament than from ints in an electrical,

7 victionnuns iinsrcn. Mention tide Ibecemher 14 1920 perm Io. 436,037.

' the positive end, the result'being that all parts of'the filamentary cathode become active at the same time. This gives a sharp ues' 'whereby a more accurate measurement of the unknown voltage may be made.

-Fonfurther details -of the invention reference maybe made to the drawings, in which Fig. 1 illustrates a circuit 'for the measurement of current employing an; improved type of tube, Figs. 2 and 3 are modified types of tubes, and Fig. 4 is a perspective view of a tube employing the electrode arrangement of Fig. 1.

, .In' the- -drawing 1 represents a source of voltage to' be measured and 2 an electrondischarge device which is adapted to be connected to the source 1 at times by the switch 3 and having the current indicating instrument 4 in its output circuit. Thev battery "5 provides current for heating the filamentary cathode 6; the battery 7 supplies space current between the cathode 6 and the anode 8; and battery 9 in connectlon with the potentiometer 10 provides a variable source of negative potentialfor l the grid 11 with. respect to the cathode 6.

As pointed out" in the Heising patent above referred to, the value oi the unknown voltage may be measured b difference in the readings on t e potentiometer 10 with the switch 3 in the two positions shown, the potentiometer 10 being calibrated in. terms of. the fall of. potential along its length as usual. r r

taking the Accordinto the present invention, all 7 portions 0 the filamentary cathode are caused to cease emitting electrons "endincidentally to emit electrons at the samemoment by tapering the grid so that the impedance to the flow of electrons ofiered by the grid is graduated in such a manner as to compensate for the fallof potential along the filament. Ordinarily the negative end of the filament, 6 starts to. emit electrons first, and last to stop emitting electrons because there is a greater potential between the negative end. of the filament and the'anode than there is betweeen the positiveend of the filament and the anode. This may be compensated for in 'several ways. As shown in Fig. 1, the grid,

which may be made up of two planary sections, or which may be "helical as shown in' Fig. 4, is arranged so that the portion of the grid adjacent the negative end of the filament is closer to that end than the positive end of the grid is to the positive end of the filament, the. varying distance between the difl'erent adjacent portions of the.

grid and filament providing the required variation in impedance to the electron flow.

The/desired variation in impedance to the electron flow along the length of the filamentmay be secured, as-shown in Fig. 2,

by maintaining the grid 12, which may be V spaced at the negative end of the filament than at the positive end thereof.

In each of the modifications the desired result is secured with a grid which is an equipotential electrode, thereby making 1t unnecessar to compensate for the cathode potential rop by a similar potential drop in the grid as is done for instance in the circuit of Langmuir Patent No. 1,273,630,

July 23, 1918.

While the improved form of tube has been described as applied to the measurement of potentials, it is of more general application.

What is claimed is: i

1. An electrondischarge device compris-' ing a multi-potential cathode, an anode and an equipotent-ial control electrode, said control electrode having parts in such space relationship to parts of said cathode as to ofier to the flow of electrons between the cathode and anode an impedance which compensates for the drop in potential along the cathode.

2. An. electron discharge device comprising a filamentary cathode, a source of ourcathode as to cause all portions of said cathode to cease emitting electrons simultaneously when said grid is given an arithmetically increasing negative potential with respect to said cathode.

3. The method of obtaining a desired rela tion between the voltage and current between an anode and a cathode having a control electrode in controlling relation thereto, which comprises gradually varying, from point to point of the cathode the impedance opposed by the control electrode to the flow of electrons from the different points of the cathode, while varying, from point to point of the cathode, the voltage from the different points of the cathode to the immediately adjacent, corresponding points of the control electrode.

4. The method of compensating for the drop in potential along a cathode having a control electrode in controlling relation thereto, which comprises offering different 'impedances to the flow of electrons from diiferent portions of the cathode while. varymg, from point to point of the cathode, the v0 tage from the different points of the cathode to the immediately adjacent, corresponding points of the control electrode.

5.- An electron discharge device comprising an anode, a cathode, and an electrode so tapered, and so positioned with respect to said anode and said cathode, as to cause the flow of electrons from different portions of said cathode to said anode to be impeded by amounts which difier in such manner as to compensate for the efiect. of the voltage drop in said cathode upon said electron flow.

In witness whereof I hereunto subscribe my name this 13th day of December A. D.,

RALPH V. L. HARTLEY. 

